nav{
	font-family: "微软雅黑";
	font-size: 20px;
	background: lightblue;
	text-align: center;
	position: sticky;
	top: 0;
	z-index: 999;
}
nav ul{
	list-style-type: none;
	display: flex;
	flex-wrap: nowrap;
	justify-content: space-between;
	max-width: 800px;
	margin-top: 0;
	margin-left: auto;
	margin-right: auto;
}
nav ul li{
	width: 150px;
}
nav ul li a{
	display: block;
	text-align: center;
	text-decoration: none;
	background-color: lightgreen;
	padding: 10px 0;
	border:1px solid #ccc;
}

